Chloroplast phylogenomics and the taxonomy of Saxifraga section Ciliatae (Saxifragaceae)

Abstract Comprising ca. 200 species, Saxifraga sect. Ciliatae is the most species‐rich section of Saxifraga s.str., whose center of diversity is in the Tibeto‐Himalayan region. The infra‐sectional classification of sect. Ciliatae is still in debate due to the high level of species richness, as well as remarkable variations of habitat, morphology, physiology and life cycles. Subdivisions of this section proposed in various taxonomic systems have not been adequately tested in previous phylogenetic studies, partly due to low taxonomic sampling density, but also to the use of few DNA markers. In order to achieve a more robust infra‐sectional classification of sect. Ciliatae, complete chloroplast genomes of 94 taxa from this section were analyzed, of which 93 were newly sequenced, assembled and annotated. The length of the 94 plastomes of sect. Ciliatae taxa range from 143,479 to 159,938 bp, encoding 75 to 79 unique protein‐coding genes (PCGs). Analyses of the 94 plastomes revealed high conservation in structural organization, gene arrangement, and gene content. Gene loss and changes of IR boundaries were detected but in extremely low frequency. The molecular phylogenetic tree from concatenated PCGs and complete chloroplast genome sequences exhibited high resolution and support values and confirms that sect. Ciliatae is monophyletic. Three well‐supported clades were revealed within the section that agree relatively well with the subsectional taxonomy of Gornall (1987), but some minor modifications should be made. Firstly, the monotypic subsection Cinerascentes should be abandoned and its constituent species, S. cinerascens, assigned to subsect. Gemmiparae. Secondly, subsections Rosulares and Serpyllifoliae should be merged and become subsect. Rosulares. Section Ciliatae thus comprises: subsect. Hirculoideae Engl. & Irmsch.; subsect. Rosulares Gornall; subsect. Gemmiparae Engl. & Irmsch.; subsect. Flagellares (C. B. Clarke) Engl. & Irmsch. and subsect. Hemisphaericae (Engl. & Irmsch.) Gornall.

A recent phylogenetic study of ca. 50% of Saxifraga species employed sequence data of the internal transcribed spacer (ITS) region of nuclear ribosomal DNA (nrDNA) and the trnL-trnF region of plastid DNA (Tkach et al., 2015). The authors recognized at least 13 sections. Among them, sect. Ciliatae Haw. is the largest, comprising over 200 species, nearly half the genus, and is the focus of the present study. The section has a center of diversity in the Tibeto-Himalayan region (THR), which includes the Qinghai-Tibetan Plateau, the Himalayas, and the Hengduan Mountains (Mosbrugger et al., 2018).
Species from the section inhabit rock faces, scree slopes, tundra, alpine meadows and woodland margins, a range of habitats similar to those occupied by species outside the section in Europe. Not surprisingly, this habitat diversity is reflected by extensive morphological, physiological and life cycle diversity. For example, habit ranges from cushions or spreading mats to tall, single-stemmed herbs; some species produce filiform stolons; some are obligate calcicoles or calcifuges; and, whilst most are perennial, some are monocarpic perennial or even annual species.
The first authors to attempt an infra-sectional classification of sect. Ciliatae in any detail were Irmscher (1912a, 1912b), who arranged what was then called sect. Hirculus (Haw.) Tausch. (= sect. Ciliatae) into 11 groups based on resemblances in gross morphology. Initially, the 11 taxa were described at subsections, although they were also referred to as greges (Engler & Irmscher, 1912a); a few months later all mention of subsections had been dropped and they were exclusively designated as greges (Engler & Irmscher, 1912b). The latter treatment was reprised in a formal monograph of the whole genus (Engler & Irmscher, 1916/1919. It is clear that it was difficult to assess the relationships among the 11 greges, as is evident from the scheme proposed by Engler and Irmscher (1912b), in which grex Hirculoideae was regarded as central and to which the other 10 greges were more or less equally related ( Figure S1). Gornall (1987) revised Engler and Irmscher's (1912b, 1916/1919, classification by recognizing the greges Hirculoideae, Gemmiparae, Cinerascentes, Flagellares and Hemisphaericae as subsections, as was originally proposed (Engler & Irmscher, 1912a); by subsuming greges Stellariifoliae, Turfosae and Densifoliatae into grex Hirculoideae (converted to series rank) and recognizing greges Nutantes and Lychnitidae as series, all within subsect. Hirculoideae; and by splitting grex Sediformes into two subsections: Rosulares and Serpyllifoliae, based on whether or not a prominent basal leafrosette is developed. In total, Gornall (1987) recognized seven subsections and six series, although no species lists were given. Shortly afterwards, in an account of the genus in China, Pan (1991Pan ( , 1992 adopted a novel approach to the classification of the species by fo- Leaving aside a number of nomenclatural issues, the resulting system was revised significantly by Pan et al. (2001), and only a single section was recognized, sect. Ciliatae, consistent with the treatment of Gornall (1987). Although the ranks of subsection and series were not used, species were accommodated in informal subgroups corresponding to seven identification keys in which leaf venation and the nature and distribution of hairs featured prominently.
Molecular phylogenetic studies have been applied to the classification of sect. Ciliatae. Zhang et al. (2008) pointed out that sect. Ciliatae as delimited by Irmscher (1916/1919) and Gornall (1987) was monophyletic, based on ITS sequences. This result was subsequently confirmed by Gao et al. (2015) using the combined dataset of psbA-trnH, trnL-trnF and ITS sequences, and three major clades were revealed: clade 1 contains species belonging to  Zhang et al., 2008;42 in Gao et al., 2015;71 in Tkach et al., 2015); and (ii) low to moderate support for some lineages because of employing only a few DNA markers.
In all such studies the contents of each of the three subclades were largely unresolved.
In this paper, we aim to improve matters by using whole chloroplast (cp) genomes. Chloroplast genomes are now widely employed in phylogenetic studies, due to their conservative character in terms of structure, gene type and gene order . Analysis of complete cp genomes has the advantage of the potential to significantly improve the resolution of phylogenetic relationships in large, complex plant lineages (Jansen et al., 2007), even in enigmatic taxa (Dong et al., 2018). In this study, we combined a high sampling density with whole cp genome sequences to: (i) reconstruct a robust phylogeny of sect. Ciliatae; and (ii) use the phylogeny to test earlier taxonomic systems and propose revisions where necessary.

| Taxon sampling
Since sect. Ciliatae as delimited by Irmscher (1916/1919) and Gornall (1987) has been shown to be monophyletic (Gao et al., 2015;Tkach et al., 2015;Zhang et al., 2008), and our main aim of this study is to address infra-sectional classification, our sampling strategy focused on taxa within sect. Ciliatae. A total of 99 taxa of Saxifraga are included, of which 94 are from sect. Ciliatae, comprising ca. 50% of the species diversity of this section (Table S1).
As outgroups, we included 17 representatives from other genera of Saxifragaceae as well as more distantly related taxa from Grossulariaceae and Iteaceae. This resulted in a final data matrix of 122 complete cp genome sequences, of which 103 were newly generated in this study (93 taxa from sect. Ciliatae; two from sect. Mesogyne Sternb. and Irregulares Haw., respectively; and six from the genus Micranthes). Leaf material was collected in the field and dried in silica gel. The taxon, locality, voucher information and Genbank accession numbers are listed in Table S1. Voucher specimens are deposited in the herbarium of Northwest Institute of Plateau Biology (HNWP), Xining, Qinghai, China.

| Sequencing and quality control
Total genomic DNA was extracted from silica-dried leaves by the DNA quick extraction system (DP321) according to the manufacturer's protocol (Tiangen Biochemical Technology Co., Ltd.). Total DNA was then randomly fragmented with the Covaris ultrasonic crusher. A series of steps were performed to complete library construction, such as end repair and phosphorylation, a-tail addition, sequencing connector addition, purification, and PCR amplification.
Finally, the qualified libraries were pooled into flowcells. NovaSeq 6000 (Illumina Inc.) was used for sequencing after cBOTs clustering, with paired-end methods (150 bp). We used fastp v.0.23.1  to filter raw sequence reads when: (i) the N content in any read was more than 10% of the base; (ii) the number of low quality (Q ≤ 5) bases in any read exceeded 50%; and (iii) any read contained the adapter content; if so, the paired reads were removed (Yan et al., 2013).
The preliminarily annotation of complete plastid genomes downloaded from GenBank may have some problems, such as format errors and a reversed SSC area, we therefore re-annotated them also with PGA. The correctness of the gene products was then manually checked for common errors, e.g. missing start or stop codons, and interrupted translation products. Finally, the modified sequence was submitted to ORGDRAW's online tool for chloroplast genome visualization (Lohse et al., 2007).
The program Gblocks v.0.91b (Talavera & Castresana, 2007) was used to remove the poorly aligned positions and divergent regions from the multi-sequence alignment results. Furthermore, individual PCGs were refined in batch using MACSE v.2 (Ranwez et al., 2018).
Individual aligned, trimmed and refined PCGs were then concatenated into a single matrix for the following phylogenetic analyses.
Phylogenetic reconstructions were conducted by means of maximum likelihood (ML) and Bayesian inference (BI) as implemented in PhyloSuite (Zhang, Gao, et al., 2020). Substitution models for the ML and BI analyses were chosen on the basis of the Akaike information criterion (AIC) using ModelFinder as implemented in IQ-TREE v.1.6.12 (Kalyaanamoorthy et al., 2017;Nguyen et al., 2015). The best fitting model was GTR + F + I + G4 for the ML and BI analyses for both data matrix of complete plastid sequences and PCGs. The ML analyses were performed using IQ-TREE with 1000 bootstrap replicates. The BI analyses were conducted using MrBayes v.3.2.6 by running for 10 million generations with four parallel Markov Chains Monte Carlo (MCMC; Ronquist et al., 2012). Samples were taken every 1000 generations and the first 25% trees were discarded as burn-in. Phylogenetic trees were visualized and embellished using the online tool ITOL v.6 (Letunic & Bork, 2007).

| Performance test of individual PCGs to species trees
To investigate heterogeneity among gene trees, sequences of each PCG were used to reconstruct individual gene trees by mean of ML.
The gene trees were then combined in ASTRAL v.5.7.8 to form a species tree with coalescence (Mirarab et al., 2014). In addition, the phylogenetic tree derived from ML based on concatenated PCGs, as mentioned above, was also employed to conduct the heterogeneity test. In total, the dataset consisted of 79 PCG trees, a gene species tree and a phylogenetic tree of the 122 taxa. The R package TREESPACE v.1.1.4.1 (Jombart et al., 2017;Zhang, Sun, et al., 2020) was employed to calculate the pairwise distances within and between gene trees and species trees, and to plot the statistical distribution of the trees by the unrooted Robinson-Foulds algorithm, following the framework of Gonçalves et al. (2019). Since TREESPACE only accepts groups of trees with the same tips, we removed the psaJ and accD locus from PCGs dataset. Finally, we conducted a principal coordinate analysis (PCoA) to analyze any inconsistency between gene trees and species trees.  Ser. (Table 1). Since the expansion and contraction of the IR region is the main cause of variation in plastome size, we classified sect.
Ciliatae plastomes into seven types (a-g) based on the changes in IR boundary ( Figure 1). All the 94 sect. Ciliatae plastomes correspond to type a, except for six which were classified as types b-g, viz.  Table S2). We detected six different repeat patterns, ranging from mononucleotide (p1) to hexanucleotide (p6). The results showed that p1 is most abundant, accounting for a proportion of 65.85%-85.45%, while pentanucleotide (p5) and p6 occurred with relatively low frequency (0%-5.8%, 0%-7.32%, respectively). A further count of the number of A/T and G/C repeats in p1 showed that the frequency of A/T repeats (37-58) was much higher than that of G/C (1-4; Figure S2). Highly divergent regions among the 94 sect. Ciliatae plastomes were assessed using mVISTA with the annotation of S. sinomontana as the reference genome. Pi values were then calculated using a sliding window method in DnaSP to further detect highly variable sites among sect.

| Phylogenetic analysis
Four phylogenetic trees were reconstructed by means of ML and BI, based on the complete chloroplast genome sequences and 81 shared PCGs. Topologies of the four phylogenetic trees were similar, except F I G U R E 1 Plastid structure of S. sect. Ciliatae, a-f represent different structural types, which are divided according to the difference of IR region. Genes located in the IR region are shown in the gray box at the bottom right.

| Performance of individual PCGs to species trees
We employed PCoA to investigate the heterogeneity of gene trees, synthetic gene species tree with coalescence, and phylogenetic tree estimated based on ML of concatenated PCGs. The results revealed that the two species trees are distributed relatively close to each other, whereas individual gene trees exhibit great variation ( Figure 4). The first and second axes of the PCoA explained 8.5% and 2.6% of the variation in tree topologies, respectively.
The gene trees using rpoB, rpoC2, ndhF, matK and ycf1 are close to gene species trees, of which the latter two are commonly used for phylogenetic studies. We provided the gene species tree with coalescence and gene trees based on rpoB, rpoC2, ndhF, matK and ycf1 in Figure S8.

| Plastome structure of sect. Ciliatae
In previous studies related to sect. Ciliatae, whole chloroplast genome data of only one species has been published .
In this study, chloroplast genomes of 103 taxa of Saxifragaceae were newly sequenced and assembled, of which 93 are from sect.
Ciliatae. Structure analyses of these newly generated plastomes  (Sun et al., 2018). Considering that gene loss in plastomes is an ongoing process in evolution (Martin et al., 1998), the extremely low frequency of gene loss in S. sect. Ciliatae may reflect a relatively short evolutionary history of this species-rich section, which has been confirmed by previous studies Ebersbach, Schnitzler, et al., 2017;Gao et al., 2015).
The boundaries of IRs and LSC/SSC differ in angiosperms (Raman et al., 2017), and expansion/contraction of the IR regions often lead to size variation of chloroplast genomes (Wang et al., 2008). In sect.

F I G U R E 4
Discordance of plastid gene trees. Principal coordinate analysis depicting ordinations of five species trees versus 79 plastid protein-coding gene (PCG) trees using unrooted Robinson-Foulds algorithms. Since TREESPACE only accepts groups of trees containing the same tips, psaJ and accD locus was removed. The two species trees and gene trees based on rpoB, rpoC2, ndhF, matK and ycf1are indicated in the plots.

| Performance of individual PCGs to species trees
Five gene trees based on rpoB, rpoC2, ndhF, matK and ycf1, show the closer to the two species trees in sect. Ciliatae. Among these PCGs, matK gene encodes the only mature enzyme related to chloroplast group II intron splicing in land plants. It is one of the most rapidly evolving genes and is widely used in phylogenetic reconstruction in angiosperms (Fan et al., 2022;Kim et al., 2019;Kuo et al., 2011;Wei et al., 2021). Ycf1 is a coding region containing long tandem repeats.
In many plant plastid genomes, the ycf1 gene has undergone widespread insertions of the tandem repeat, leading to extreme length variation. These characteristics make this gene one of the most valuable markers in phylogenetic studies (Duan et al., 2020;Khandelwal et al., 2022;Li et al., 2021). The sequences of the five genes are relatively long, which can provide more effective resolution in phylogenetic analyses. It is worth noting that the phylogenetic inconsistency of individual gene trees is serious, emphasizing the importance of taking gene tree heterogeneity into account in phylogenetic studies.

| Phylogenetic and taxonomic inferences in sect. Ciliatae
A total of 94 taxa of sect. Ciliatae are included in this study, representing 83 species and 11 varieties. This species sampling consists of about half of the species of sect. Ciliatae and represents nearly all subtaxa as proposed by Irmscher (1916/1919), Gornall (1987), Pan (1991Pan ( , 1992 and Pan et al. (2001). It is thus the most complete molecular phylogenetic investigation of sect.
Ciliatae carried out so far, especially at the level of plastomes.
As has been shown in previous studies (Gao et al., 2015;Tkach et al., 2015;Zhang et al., 2008), sect. Ciliatae as delimited by Engler and Irmscher (1916/1919), Gornall (1987 and Pan et al. (2001), is a monophyletic group. The three main clades within sect. Ciliatae as revealed by this study are similar to those recovered by Gao et al. (2015) and Tkach et al. (2015), but with higher support values and much better resolution within each clade. The three major clades of sect. Ciliatae correspond reasonably well to subtaxa postulated in previous taxonomic systems based on morphological characters (Engler & Irmscher, 1912a, 1912bGornall, 1987;Pan et al., 2001), though with some exceptions. Based on our relatively large number of sampled taxa and comparatively well-resolved and supported phylogenetic tree, some taxonomic issues can be addressed.

| Clade 1
Clade 1 comprises species from subsects. Hemisphaericae, Flagellares, Gemmiparae and Cinerascentes, as well as S. brevicaulis H. Sm. It is not clear how this clade as a whole can be recognized morphologically.
It is divided into two well-supported subclades. The first of these, subclade A, comprises basal taxa that are successively sister to a monophyletic group of species characterized by filiform stolons. The basal taxa include S. brevicaulis and S. hemisphearica, to which may be added S. eschscholtzii Sternb. (Tkach et al., 2015). The latter two species formed subsect. Hemisphaericae (Engler & Irmscher, 1912a, 1912b, characterized in part by hyaline, fimbriate leaf apical margins. Pan (1991Pan ( , 1992 added S. zhidoensis J-T. Pan and S. perpusilla J.D. Hook. & Thoms to this group. DNA sequence data shows that S. zhidoensis may also be one of the basal taxa since morphologically it is very similar in all respects to S. hemisphearica. In Gao et al. (2015) it clustered with the sister group of stoloniferous species, although support was not very strong and sampling was poor. The placement of at least S. hemisphaerica and S. zhidoensis alongside species from subsect. Serpyllifoliae (key 7 in Pan et al. (2001)) is not supported by our data, since all representatives of subsect. Serpyllifoliae belong with species of subsect. Rosulares to form a well-supported clade (clade 2; BS = 100%, PP = 1.00). In contrast, sequence data from this study and from Tkach et al. (2015) shows that S. perpusilla belongs squarely in clade 2, a group comprising sections Serpyllifoliae and Rosulares.
The inclusion of S. brevicaulis H.Sm. among subclade A comes as a surprise. Despite its lack of chalk glands, this white-flowered species firstly assigned to section Porphyrion (which always has these structures but very many of whose species have white flowers). Zhang et al. (2015) moved it to sect. Ciliatae on account of its pollen morphology. S. brevicaulis was put in key 7 by Pan et al. (2001), corresponding to Gornall's subsect. Serpyllifoliae, but in our analyses it clusters at the base of subsect. Hemisphaericae and subsect.
Flagellares with high support values. This species exhibits a cushionlike habit and a setose-ciliate apical margin of its basal leaves, somewhat similar to species of subsect. Hemisphaericae. Its close relatives, S. sessiliflora H.Sm. and S. williamsii H.Sm. (not studied here), may also belong here. Relationships among the taxa basal in subclade A need to be investigated further with improved taxonomic sampling but, for the moment, we prefer to retain subsect. Hemisphaericae as a convenient name under which to house these species.
The remaining part of subclade A comprises a monophyletic group of species with axillary, filiform stolons. These can be recognized as subsection Flagellares (Clarke) Engler and Irmscher (1912a), as in Gornall (1987) and in key 1 by Pan et al. (2001). We sampled five of the estimated 18 species of this subsection. With the exception of S. brunonis, sampled representatives of subsect. Flagellares form a clade highly supported as sister to S. hemisphaerica. The errant S. brunonis, despite possessing filiform stolons, occupies a position embedded among species of subsect. Gemmiparae in both this and in previous phylogenetic studies (Gao et al., 2015;Tkach et al., 2015).
This suggests a parallel origin of axillary filiform stolons, a character that also occurs in the distantly related S. stolonifera Curtis of sect.
Microgynae. The dramatic separation of these taxa into two sections is here shown to be unwarranted: support for an inclusive subsection Eleven out of 20 species were sampled for this subsection, including a recently published species, S. viridipetala Z-X. Zhang & Gornall (Gao et al., 2018). All representatives of subsect. Gemmiparae form a well-supported monophyletic lineage in which S. brunonis and S. cinerascens are embedded. Species of subsect. Gemmiparae can be recognized by their leafy axillary buds (Engler & Irmscher, 1912a, 1912b, 1916/1919, although these can occasionally be missing. The filiform stolons in S. brunonis may be interpreted as developments of the leafy buds. The main distribution range of this subsection is the Himalaya-Hengduan Mounatins region.

Saxifraga cinerascens is a narrowly distributed species restricted to north-western Yunnan. It is the only species in subsection
Cinerascentes and is recognized by its well-developed leaf rosettes, cartilaginous setose-ciliate leaf margin and aristate leaf apex (Engler & Irmscher, 1912a, 1912b, 1916/1919. Gornall (1987) initially accepted the subsection. Pan (1991Pan ( , 1992, however, assigned the species to subsect. Gemmiparae Engl. & Irmsch., a position reaffirmed by Pan et al. (2001) who placed it in their key 2, which corresponds to subsect. Gemmiparae. A previous molecular phylogenetic study by Gao et al. (2015) also suggested that S. cinerascens is nested within subsect. Gemmiparae, a result supported by the present study. In fact, close examination of specimens shows that the species produces axillary leafy buds (diagnostic of the subsection) at proximal nodes, but these develop into sterile shoots by anthesis. Thus, it is convenient to abandon subsect. Cinerascentes and put S. cinerascens in subsect.

| Clade 2
This well-supported clade consists of all species belonging to subsections Rosulares Gornall and Serpyllifoliae Gornall. We sampled 25 out of ca. 60 species of this group. This clade corresponds to Irmscher's (1916/1919) (1832) and therefore illegitimate. Gornall (1987) split this group into two subsections, subsect. Rosulares and subsect. Serpyllifoliae, based on whether a well-defined basal leaf rosette was produced or not.
From a habit viewpoint, species of subsect. Rosulares exhibit a cespitose habit, while plants of subsect. Serpyllifoliae are more mat-like.
Our plastome data presented in this study indicate that Engler and Irmcher's original taxon is monophyletic, and corresponds quite closely to Pan's (1991Pan's ( , 1992 delimitation of subsect Rosulares. Thus, the division into two subsections by Gornall (1987) is not supported by this study and the two are best amalgamated. Its name should be subsect. Rosulares Gornall, as selected by Pan (1991). The morphological synapomorphy of this subsection might be leaf rosettes either at the base of plants or terminal on sterile shoots. Pan (1991Pan ( , 1992 divided the clade into six series, but comparison of his lists of included species against the phylogenetic tree ( Figure 2) shows that none of his series is monophyletic. The lumping approach adopted by Pan (1991Pan ( , 1992

| Clade 3
The third main clade recovered in our study, which is sister to clade 2, corresponds to subsect. Hirculoideae Engler and Irmscher (1912a), as delimited by Gornall (1987). It is the most species rich subsection of sect. Ciliatae, comprising more than 100 species of which we sampled 50 taxa. This clade has been identified in previous phylogenetic studies (Gao et al., 2015;Tkach et al., 2015;Zhang et al., 2008). Two morphological synapomorphies can be recognized for this subsection: (i) brown-crisped hairs present at least at the proximal nodes of the stem (Engler & Irmscher, 1912a, 1912b; (ii) trinucleate pollen (Zhang & Gornall, 2011). As was described by Gao et al. (2015), three sub-groups can be identified on morphological grounds: (i) species with brown-crisped hairs on the pedicels (corresponds to key 3 of Pan et al., 2001); (ii) species with leaves having a glaucous abaxial surface and a prominent submarginal vein (corresponds to key 5 of Pan et al., 2001); and (iii) the remainder (corresponds to key 6 of Pan et al., 2001). In this study, our phylogenetic results indeed reveal three well-supported subclades, but they correspond only partially with the morphological groups. Species with the three above-mentioned characters are to some extent mixed on the phylogenetic tree. Pan (1991Pan ( , 1992 recognized six series and four subseries to accommodate the species, based on sepal vestiture, sepal and petal nervature and presence and number of calloses. None of them is monophyletic when compared to our tree (Figure 3), apart from two for which it is not possible to tell based on the current taxonomic sampling. Further morphological and micromorphological studies combining phylogenetic results with a wider sampling are needed to reveal species relationships of this species rich subsection.
It is worth mentioning that this paper reconstructs the phylogenetic relationships of sect. Ciliatae merely based on chloroplast data.
Although only few hybridizations have been recorded in this taxon, this does not mean that hybridization has never occurred, as well as influencing the evolutionary history. We will discuss the possible conflicting phenomena between nuclear and plastid phylogenies in the future research.

| Taxonomic conclusions
The plastome phylogenetic results of sect. Ciliatae mostly agree with the classification of Gornall (1987), but some minor modifications should be made: (i) subsection Hemisphaericae requires further investigation, with better taxon sampling to establish its phylogenetic status and limits; (ii) Subsection Gemmiparae should include subsect. Cinerascentes (S. cinerascens); (iii) subsections Rosulares and Serpyllifoliae should be merged into one large subsection, for which the correct name is subsect. Rosulares Gornall. Section Ciliatae Haworth thus comprises at least five subsections as follows.

| CON CLUS IONS
In this study, we successfully sequenced the complete chloroplast genome of 103 taxa, including 97 of Saxifraga and six of Micranthes.
Combined with the NCBI database, the plastid genome data of 94 taxa of sect. Ciliatae were obtained. It is, up to now, the larg-

CO N FLI C T O F I NTE R E S T
None declared.

DATA AVA I L A B I L I T Y S TAT E M E N T
DNA sequences: Genbank accessions ON720850-ON720952.